Introduction
Luciferase is the alpha-beta heterodimer monooxygenase enzyme
responsible for catalyzing the light producing oxidation reaction
in luminescent bacteria. Its official name is alkanal monooxygenase
(EC 1.14.14.3), but I'm sure that it would prefer being called
luciferase since that makes it sound like one tough enzyme. The
substrate that a luciferase acts on is generally called luciferin
(for more information on this general interaction, feel free to
jump on over to the bioluminescence section of this site); in the specific case of bacterial luciferase,
the specific substrates which the enzyme acts upon are reduced
riboflavin 5'-phosphate (FMNH2), long-chain aliphatic aldehyde (R-CHO), and of course, molecular
oxygen. The products of the reaction are FMN, H2O, and visible blue-green light (490 nm). Bacterial luciferase
is a unique flavoprotein in that it utilizes reduced flavin molecules
as substrates instead of using them as tightly bound co-factors.
The reaction scheme is shown below, with an accompanying description
of the reaction steps involved.
Luciferase Reaction Scheme
Figure adapted from Biochemistry (4)
The first step of the reaction is the activation of luciferase-bound
N (1)-deprotonated FMNH- by O2 to form the FMN-4a-hydroperoxide intermediate (II). Subsequently,
the aliphatic aldehyde reacts with intermediate II, resulting
in the formation of the FMN-4a-peroxyhemiacetal intermediate (III).
Both an alkylhydroxyoxy radical and a FMN-4a-hydroxide intermediate
(IV.) radical are then formed due to the intermolecular electron
transfer within intermediate III. The alkylhydroxyoxy radical
then undergoes a transformation into a carbon-centered alkylhydroxy
radical and donates its extra electron to intermediate (IV.).
As a result, RCOOH as well as FMN-4a-hydroxide (IV*), which has
been induced into an excited state, are formed. The excited state
intermediate eventually decays and produces light and brings it
to its ground state (IV); finally, via dehydration, the ground
state IV molecule yields FMN and H2O. An alternate path exists in which intermediate II, rather
than reacting with the aldehyde, undergoes a dark decay to produce
FMN and H2O2 without the release of light energy. (5)
Well, there's more to be told about luciferase, so why don't you
click on the icon below...?
You can't quit now, by golly, you're learnin' so much...!
On to Luciferase Structure & Active Site
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